Development and use of a simplified WBGT estimation chart for indoor environments

Abstract

地球温暖化の進展の影響もあり，近年ますます夏季の猛暑が著しくなっている。熱中症に被災する人は年々増加の一途を辿っており，熱中症防止対策は喫緊の課題となっている。熱中症防止対策用の暑熱環境評価方法として，WBGT（湿球黒球温度）が労働分野，スポーツ分野，学校教育現場や一般生活環境でも広く用いられている。WBGTを測定するためには，WBGT測定器が必要であるが，熱中症が多く発生している一般生活環境では，WBGT測定器がない場合がほとんどである。一般生活環境の大半を占める日射のない室内において，気温と相対湿度からWBGTを推定するツールとして，2008年に日本生気象学会より「WBGT簡易推定図」が開発・公開された。この簡易推定図は広く用いられてきたが，日射のある環境で過小評価すること，日射のない室内では過大評価することが指摘されたこと，ならびに簡易推定図に適用範囲が明記されておらず，簡易推定図の転載により推定図のみが独り歩きし，誤用される危険性があること等の理由で，改訂が急務となった。このことから，日射のない室内のみに適用可能な改訂版の簡易推定図を，熱収支理論に基づいて開発し，2022年に公開した。改訂版の簡易推定図は，実環境との比較の結果，日射のない室内では非常に精度良く推測することが可能であった。改訂版の簡易推定図ならびに，簡易推定図が掲載されている「日常生活における熱中症予防指針」は，熱中症が多発している室内環境における熱中症対策に極めて有用であると考える。

Translated Abstract

Wet Bulb Globe Temperature (WBGT) is widely used in fields of labor, sports, school education, and general living environments as an informative parameter for preventing heat disorder. A WBGT measuring device is required to obtain this value. In general, in living environments where heat disorder often occurs, WBGT measuring devices are almost unavailable. In 2008, the Japanese Society of Biometeorology developed and released a “Simplified WBGT estimation chart for indoor environments” as a tool for estimating WBGT based on air temperature and relative humidity. This estimation chart has been widely used, but it underestimates WBGT in environments with sunlight and overestimates this value in indoor environments without sunlight. A risk of misuse has also been found in that the range of applicability of the simplified estimation chart is not clearly stated. A revised estimation chart, which can only be applied to indoor environments without sunlight, has thus been developed based on heat balance theory and released in 2022. This revised estimation chart was able to make very accurate estimations in indoor environments without sunlight as assessed by comparing it with actual WBGT measurements. The revised version of the estimation chart is extremely useful for countermeasures against heat disorder in indoor environments where heat disorder is common.

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